Objects to be thawed are made by collecting a plurality of marine products such as shrimps and shellfishes or the other products, especially food materials, and freezing them in a block shape. Apparatuses for thawing such objects to be thawed have been known, such apparatuses including a vacuum steam thawing apparatus for thawing objects to be thawed by containing them in a sealed process tank under reduced pressure and supplying steam into the process tank (Please refer to Patent Publication 1 below); a thawing apparatus for thawing objects to be thawed in a thawing tank containing water by ejecting a gas, made by mixing overheated steam with air, from a bottom of the tank (Please refer to Patent Publication 2 below); a thawing apparatus for thawing objects to be thawed in a thawing chamber by flowing high-humidity steam toward the objects (Please refer to Patent Publication 3 below); a microwave thawing apparatus for thawing frozen foods by irradiating the frozen foods with microwaves (Please refer to Patent Publication 4 below); and a thawing apparatus for thawing objects to be thawed in a thawing tank containing water by merely supplying water from a bottom of the tank to utilize convection in the tank (Please refer to Patent Publication 5 below).
Patent Publication 1: Japanese Patent Laid-open Publication No. 2004-357627
Patent Publication 2: Japanese Patent Laid-open Publication No. 2005-052022
Patent Publication 3: Japanese Patent Laid-open Publication No. 2004-201597
Patent Publication 4: Japanese Patent Laid-open Publication No. 2002-218959
Patent Publication 5: Japanese Patent Laid-open Publication No. 7-030082
In the thawing apparatuses disclosed in Patent Publication 1-4, a block-shaped object to be thawed including a plurality of frozen articles is continuously subjected to physical energy until the object has been thawed thoroughly. Concretely, such physical energy is steam in the Patent Publication 1, gas made by mixing overheated steam with air in the Patent Publication 2, high-humidity air in the Patent Publication 3 and microwaves in the Patent Publication 4. In this connection, although articles near a surface of the block have been already thawed in an earlier period after the thawing process starts, they continue to be subjected to the physical energy until the object is thawed thoroughly. Thus, the articles thawed in the earlier period may be damaged; for example, they may be broken into small pieces or their characteristics changed. As a result, there may be a difference in quality between articles thawed in the earlier period and those thawed in a final period and thus articles having a uniform quality cannot be obtained. In order to overcome this problem, there is a device for taking earlier thawed articles out before later thawed articles. However, not only a mechanism of such a device but also operation and maintenance thereof are very complicated
Since the apparatus disclosed in the Patent Publication 5 merely causes convection of water, thawed articles may possibly not be damaged than those in Patent Publications 1-4. However, it takes much time to thaw an object to be thawed and thus the apparatus is not efficient.
It is therefore a first object of the present invention to provide a method of and an apparatus for efficiently thawing objects to be thawed without damaging them.
Further, it is a second object of the present invention to provide a method of and an apparatus for uniformly thawing a block-shaped object to be thawed including a plurality of frozen articles.